1. Field of the Invention
The present invention relates to an antenna device for use in an RFID system, a near field radio communication system, or the like, and an electronic apparatus including the antenna device.
2. Description of the Related Art
In recent years, a small-size radio communication apparatus such as a cellular phone terminal has been equipped with an RFID system with a 13.56 MHz band such as an NFC (near field radio communication system) in increasing cases. An antenna to be used therein is generally a planar coil antenna, and is attached on the surface of a resin casing of a cellular phone terminal.
However, when the distance between a planar antenna coil and a circuit board included in a cellular phone terminal decreases with thinning of the cellular phone terminal, deterioration of antenna characteristics due to unnecessary coupling between the antenna and the circuit board becomes a problem.
As one antenna device that solves the above-described problem, International Publication No. 2007/060792 discloses an antenna device in which a plurality of coil units each including a winding wound thereon are disposed on side surfaces at both sides across a virtual center line of a cellular phone terminal, and the winding of each coil unit is connected via a conductor such that the winding direction of the winding of each coil unit is the same.
The antenna device disclosed in International Publication No. 2007/060792 has a problem that a plurality of null points (insensible points) occur in a region facing a principal surface of the cellular phone terminal, and thus has a problem that the usability is poor.